The invention relates to an ink jet image producing device for the reproduction of digital image data of photographic images and to a process for the control of an ink jet image producing device.
Conventional ink jet printers generally use three base colors to produce color reproductions of images. Cyan, Magenta and Yellow are generally used as the base colors. An even larger color pallet can be achieved when black is added as a further printing ink. In order to achieve a better color resolution, special ink jet printers also use 6 or even 8 colors, for example in the professional production of billboards or the like. The use of a certain paper is also important, since the color impression to the observer is also strongly dependent on how a printing medium absorbs ink, or how the ink flows on the surface of the printing medium and thereby mixes or bleeds.
On the other hand, it is possible to produce a desired color which is to be produced by way of an ink jet printer by different mixtures of the base colors present in the ink jet printer. Diverse colors can thereby already be produced by different mixtures of only three base colors. With more than three printer colors, such as 6 or 8 printer colors, the color reproduction possibilities are again multiplied. Many different color sets can thereby be computed for the reproduction of one and the same color. However, although those colors are the same according to color measurement technology, they can generate a different color impression to the human eye. This is additionally also determined by the surface quality, the absorption behavior and other quality parameters of the printing medium, such as a photographic paper or the like.
It is therefore an object of the present invention to overcome as much as possible the disadvantages of the prior art.
It is especially an object to provide an ink jet image producing device which provides an optimal color impression to the observer.
It is further a preferred object to reproduce the desired colors with a minimized amount of ink material.
It is a further object according to the invention to optimally reproduce so called memory colors which are also referred to as xe2x80x9cmemory colorsxe2x80x9d.
In a preferred embodiment, an ink jet image producing device with the features according to the invention includes a printing head with more than three base colors or more than three ink jet print colors which stretch a color space. A processing device is provided for calculating the location or color coordinates of color values of the image data in the color space. Furthermore, a determination device is provided to determine with which base or ink jet print colors or mixtures, and especially which color densities thereof, altogether referred to asxe2x80x94color setxe2x80x94, the color data of the image data can be reproduced, whereby in general several possible color sets are determined. Furthermore, a threshold device is provided which includes at least one threshold for a degree of coverage of at least one printing medium, whereby an evaluation device is provided which evaluates whether a determined color set requires a larger ink amount or a smaller ink amount, for reproduction especially on a specific, preselected printing medium. The threshold device thereby selects one of the color sets depending on the threshold for the printing medium used and the image data are printed by way of the printing head with the selected color set by using a printing head control device.
In another preferred embodiment in accordance with the invention the device includes an arrangement with at least three printing heads with respectively at least one base color instead of at least one printing head with more than three base colors. The at least three printing heads are then controlled corresponding to the otherwise at least one printing head with more than three base or print colors.
The invention also provides a process in the form of software, for example, on computer readable data carriers or in the form of a computer readable electromagnetic wave constellation.
It is possible in accordance with the preferred process of the invention to select a specific color set from many possible color sets depending on the properties of a respectively used printing medium and depending on the desired color as well as the corresponding color density. For example, when a less strong color is to be applied, a color set can be selected for the production of this color which leads to the printing of as large as possible a surface of the printing medium.
Furthermore, when a strong color is applied which itself has a high color density, it is possible to print it out with the use of a small amount of ink, if the absorption capacity of the printing medium is also limited.
This approach has also the advantageous aspect that on the one hand somewhat higher color densities can be produced, while on the other hand the amount of ink applied can be used more effectively. Moreover, the printing speed can be increased, since because of the smaller amount of ink used a faster drying of the ink on the printing medium is achieved, thereby allowing for the application of a larger amount of information within the same time frame, which can contribute to the reproduction of a larger image surface per unit time.
The present invention can play a very special role when a large number of base or printer colors are used, so that the number of available color sets is further increased. More than one threshold value can also possibly be used for a specific printing medium in order to optimally consider the behavior of the printing medium relative to the different color sets with different amounts of applied ink.
A preferred ink jet image producing device in accordance with the invention which can be used especially advantageously further includes an image data analysis device for determining whether the image data include key memory colors, so called xe2x80x9cmemory colorsxe2x80x9d. If that is the case, a memory color assignment device which assigns the determined color image data which fit the memory color to that color set or ink of a color set which comes closest to the memory color. During the printing out of the image data, the printing head control device preferably controls the at least one printing head using the assignment result of the memory color assignment unit.
An especially good reproduction result can be achieved in this matter for colors which are especially engrained in the human memory, such as human skin color, sky blue, street gray, or the like, in that a color set or directly a corresponding ink is used for the printout of these colors which directly corresponds to the memory colors or come especially close thereto. The above mentioned threshold value can here also be used, when, for example, several color sets are possible for the reproduction of the corresponding memory color.
In order to identify the memory colors, a color analysis of the image data of an image is preferably carried out by which, based on probabilities, it is determined which color in an image corresponds with high probability to a memory color. On the other hand, it is also possible to carry out a pattern detection to identify memory colors. One can thereby, for example, search for a facial pattern in an image in order to determine with high probability, if not even with certainty, for subsequent processing in accordance with the invention, whether human skin as carrier of a memory color is present in an image.
According to a further aspect of the present invention, an ink jet image generating device is provided, the advantages of which are based on that memory colors are determined from an image data set and then a color set is selected for the printout of these memory colors especially truly reproduces the color. A threshold value (or several threshold values) is preferably also used dependent on the printing medium used, for again selecting, if several equally suitable color sets are possible, a color set which provides for an optimized color reproduction using the lowest possible amount of ink, and thereby allowing a higher printing speed or faster drying, or when the color to be reproduced has a low color density, preferably using a color set which requires a large amount of ink.
A transformation device is preferably provided with respect to both aspects of the present invention, which transforms the image data using the selected color set or the selected ink into printing head control data which are supplied to the printing head control device.
In order to further achieve an improved reproduction of the colors, several printing heads are preferably provided which are respectively controlled using their respective base colors in order to provide an optimized color reproduction.
A relatively simple model of a printing head with only three print colors is thereby preferably used, for example, when only those color image data are output which can be optimally printed with the print colors present in this printing head. A further color set is then preferably made available through an immediately downstream further printing head which also only has three print colors available, but which are different from the first three colors and which again can be printed optimally or optimized by this further printing head. Therefore, a multitude of different color sets can be provided with comparatively primitive printing heads arranged directly in series of one another with respectively different colors, and at the same time these respective printing heads preferably include colors which are closely adjacent to memory colors or identical thereto.
Conversely, a printing head with many colors can be used, whereby color sets can be combined from the diverse colors or base colors in order to stretch several color spaces. A printing head with, for example, ten colors can provide about 3 or 4 combinations of respectively n colors (with n between 3 and 9) for the stretching of respective color spaces.
Depending on the existence of memory colors, more complex printing heads can also be used on their own with 4, 6 or 8 print colors depending on the colors to be reproduced.
In order to provide even more different colors and color graduations, a diluent is preferably used in one or more printing heads.
According to a further aspect of the present invention, processes are provided for the realization of an ink jet image producing device for the printout of image data of photographic images with a printing head for more than 3 base colors or ink jet print colors. Also, it must be recognized that computer, which are used for more general purposes, can be programmed accordingly for carrying out the computer or data structure related tasks of one or more of the subunits of the device of the invention. Such a computer preferably includes a processing device for calculating the location or color coordinates of color values of image data in a color space, and preferably fulfills the functions of the determination device, the threshold device, the evaluation device, the image data analysis device, and so on, so that a conventional computer with a correspondingly equipped, possibly also conventional ink jet printer can be equipped according to the present invention and can preferably be used to provide the advantages of the invention at least to a large degree.
According to the invention it is a preferred aspect of the process that the properties of the printing medium to be printed be known, so that a threshold value or several threshold values can be selected for the determination whether a printing medium used needs to be covered with a high or low degree of coverage of an ink volume. The threshold for a color which requires a low color density is thereby selected so that as large a surface as possible of the printing medium is covered, while when a color tone with high color density is to be produced, the amount of ink to be applied is kept as small as possible. This saves ink on the one hand and allows for an increase in printing speed on the other hand by reduction of the amount of ink applied, since the shorter application and drying times contribute to an acceleration of the print production.
According to a second preferred process according to the invention, the image, data are directly searched for memory colors or image patterns, such as patterns, in order to qualify certain image regions for the reproduction with a color set or ink which is closest to a memory color or directly corresponds therewith.
It will be apparent to the person skilled in the art on study of the present disclosure, that this invention can also be used to more advantageously carry out color applications in other printing techniques or reproduction techniques. For example, one can correspondingly proceed for offset printing even when rotation offset printing machines are used. A corresponding software by which computer outputs or image reproductions on screens can be revalorized is also part of the invention. Accordingly, the attached claims are intended to cover these objects.
All combinations of image or color processing disclosed herein can be applied at different locations in the same image depending on the image content. That means the above or below disclosed processes can be used in combination, for example, for images including regions with colors of different threshold values on the one hand and regions with memory colors on the other hand.